Modified R80 G/S Sudden acceleration problem! HELP NEEDED..

[tobyyarwood]

I have recently bought a 27 year old R80 G/S which has a 1000cc conversion and four spark plugs. After riding 120 miles two days ago with no problems, yesterday after a short run in the morning the bike, quite suddenly refused to rev. properly and will not accelerate past a certain point. The engine sounds as though it is 'choking' - like it cannot breath or has no fuel when I open the throttle.. Throttling harder makes no difference - the sound gets deeper like i have pulled the choke rather than the throttle.. In neutral it has trouble too and backfires a bit. I was able to ride home with no problems as long as I accelerated VERY gently..?!

At first I thought it was a blocked fuel line as there is some gunk in the tank bottom, so I opened and cleaned the float chambers bu to no avail. Fuel seems to be getting through fine although the LH chamber was lined with ochre coloured powdery stuff..

The bike had been standing for 6 months before I bought it and at first smoked a lot - the previous owner had WD40'd everywhere. This smoke stopped and only had a final burst when i was going up a STEEP hill during the long run..

The bike has loads of mods. R100 (I think) twin disk forks, ALL NEW wiring, a kickstart that nobody can successfully use, a HUGE rear frame for two really heavy STEEL Swiss ammo box panniers..

I am due to carry out a full service, the oil has been clean and steady at half way on the dipstick and there are no leaks other than a very small dirty film over the front of the carbs but I cannot readily see where it is coming from..

Could anyone help point me in the right direction for some diagnostic tests? Or tell me that it is something very common and easy to sort out..?

Toby.

ps. I have the bike as a first boxer to try out for a VERY LONG overland adventure in about 20 months time, so want to learn how to do all my own repairs, maintenance etc. as well as decide whether such a big machine is for me - I am quite small - so far I have succesfull replaced an over-engorged clutch thrust piston and fitted a Halfords £12 speedo to verify that the OEM one is reading 10 - 20% over.. Oh, and I am in North Dorset..

 

[nick.ct]

Welcome

Your best thing right now is to subscribe to this Forum for the full benefits

Nick

PS There is so much help available from the tossers here that they'll have it all sorted in no time

 

[MattW]

Others will doubt chip in with excellent advice, but it might be worth taking off the carb tops and checking the diaphragms.

cheers
Matt

 

[(RIP) Proff]

MMMMM 27 years, could be one of the last Leaded bikes.
Check your valve clearances, if exhaust is tight you have recession, so need to get unleaded valve seats fitted or use additive.
Not an expensive job really.
Mine cost £65 the pair including seats...in 2004

 

[MATKAT]

Chokes

Might sound daft but have you checked the chokes are coming off when you close the lever. My 80GS(no one has seen it yet) had exactly the same problem from being stood for a few months, well a couple of years

 

[Rob Farmer]

Others will doubt chip in with excellent advice, but it might be worth taking off the carb tops and checking the diaphragms.

cheers
Matt

 

[MattW]

Hey, I just had my first good idea

No airhead experience, but I had on old Saab that used to eat carb diaphragms with exactly these symptoms.

 

[tobyyarwood]

Thanks everyone!

Thanks for all the ideas everyone! Am now subscribed and going to check the carb diaphragms.. air filter seems fine though I may clean und replace the k&N spare.. It never occured to me about Unleaded/leaded.. I just assumed.. I will check it out, and have written to the previous owner about the twin-spark plug conversion.. phew.. off to watch start of The Wire season 5 now.. thanks again, Toby

 

[Steptoe]

Others will doubt chip in with excellent advice, but it might be worth taking off the carb tops and checking the diaphragms.

cheers
Matt

That was my reply to the same question from the same person this morning on Horizons

 

[Kenny]

I would think that someone who has had the heads off to twin plug them would also have had the valve seat replaced. All BMW's after 1985 had unleaded heads as standard.

Oh and I'd stick to a genuine air filter ( get a full srvice kit from Motorworks/motobins/jamessherlock etc etc and you can't go wrong )

And yes, carb diaphragms and ensure the choke cables are backing right off as stated earlier.

Ignore MATKAT..he usually trashes his GS's anyway

PS Even worth emptying the float bowls and filling them with carb cleaner and then crank her over to flush out the carbs.

 

[Colt]

sounds an interesting bike,any pics?
is it the hopkins bike,as seen at horizons?

Sounds like the classic symptoms of a split/torn carb diaphram . Or maybe both sides.

running lean perhaps?it has the 1000 heads,perhaps the carbs have been played with.
ps the kickstart should be fairly easy when warm,mine is.

 

[tobyyarwood]

Yep! asking all over..

That was my reply to the same question from the same person this morning on Horizons

Yes it was me..

 

[tobyyarwood]

Yes it is that bike..

sounds an interesting bike,any pics?
is it the hopkins bike,as seen at horizons?

Sounds like the classic symptoms of a split/torn carb diaphram . Or maybe both sides.

running lean perhaps?it has the 1000 heads,perhaps the carbs have been played with.
ps the kickstart should be fairly easy when warm,mine is.

Golly! you are the 4th person i've come across who has heard of my bike.. 'The Hopkins Bike' sounds a bit ominous..

ty

 

[MattW]

Golly! you are the 4th person i've come across who has heard of my bike.. 'The Hopkins Bike' sounds a bit ominous..

ty

Looked at those diaphragms yet? - I'm on the edge of my seat

 

[tobyyarwood]

Diaphragms seem ok!! Carbs fouled.. um..

Having taken an hour from work while no-one was looking I have taken of the tops of my carbs - which are from a R100 or GS100 it seems - and the diaphragms seem fine.. although the LH bowl was and still is fouled by silty mess! I am getting a full service and overhaul kit anyway this week, from Motorworks, and emptying and cleaning my tank and the tap filters.. any ideas as to what is causing problem if the d's are ok? I held them up to the light and they have no holes or tears.. tybow

 

[bustupbiker]

Looks as if it's been under water to me! you will have to give the dagafragams

a little pull all around, it only needs a tiny pin hole. Oh! i do hope those cracks don't go all the way through the carb body, have you checked?

 

[(RIP) pastyman]

I know Ive pointed this out before but check that the little round plug in the top of the carb is not leaking. Certainly the rust looking stuff would seem to indicate that something is getting in there and it could be through these caps.

 

[tobyyarwood]

carbs so far..

Hello thread, All ok, so far as I have got, which is to remove and clean out the LH carb using the Haynes manual as a guide. It was very dirty with black stuff as well as the ochre powder stuff in the vacuum chamber. The jets were dirty but not actually blocked; but the large screw hole where the main jet holder goes was fouled up with granular black oily stuff!! I cleaned it all out very carefully with a soft brush and a lint-free cloth. There was so much that I thought it was a disintergrated rubber ring, but the Haynes manual mentions none there. I have not disturbed any of the screw settings - the carb top is still on the bike with cables attached. Although the seals, gaskets and diaphragm seem ok I will replace them. Tonight I will do the same to the RH carb which looks less bad at the top.. Oh, and the petrol taps were dirty but not clogged.. I also need to clean out the big plastic tank, hooray! Thanks for all comments, some pics below, anyone know why the tank is covered in BLACK PAINT like stuff on the underside? and how did it get all scratched off?.. ty

 

[Rob Farmer]

That may be Terry Ryans old tank. I think it was painted black and marked up with Unicef stickers when he got it from a German. Not sure though because my memories not what it was

Send Terry a PM

 

[tobyyarwood]

Seems done!!

Thanks everyone for all the good advice! I think I have cleaned out the carbs well enough and they all work when back together again! That was my day off!! Now back at school so I won't have a PROPER run now 'til next weekend!!

- - apologies for cross postings, this was my first cry for help so I cried LOUDLY. I will have more questions, hopefully of a less worried nature, as the bike is rather no-standard and I plan to get to know it mechanically as best as I can before riding it all over the planet.. and hopefully will put some details of my bike etc up on tobyyarwood.com when I can [it is very out of dat now, having my vanvan on it still!! Thanks again for all the time and advising.. this is how much workshop i have.. ty